There is a growing movement, driven by both industry and academia, towards a new network control paradigm called Software-Defined Networking (SDN). In Software-Defined Networking (SDN), a control plane implements and maintains the control logic that governs the forwarding behavior of shared network switching elements on a per user basis. A virtual network that is implemented for a tenant of a hosting system is a good example of an SDN. The virtual (logical) network of a tenant of the hosting system connects a set of data compute nodes (e.g., virtual machines) that are assigned to the tenant, to each other and to other virtual and/or physical networks through a set of logical switches and logical routers.
One of the challenges in today's hosting system networks is extending the virtual networks (e.g., of one or more tenants) to other physical networks through hardware switches (e.g., third-party hardware switches) by enabling the hardware switches to implement logical L2 and L3 forwarding elements.